International Journal of Innovative Research in Advanced Engineering (IJIRAE) ISSN: 2349-2163
Volume 1 Issue 10 (November 2014)
www.ijirae.com
A NEW SOFT SWITCHING SCHEME FOR POWER
FACTOR CORRECTION IN UPS BASED
APPLICATION
I.Mahendravarman1, A. Ragavendiran2, M.Arunprakash3 and S. Preethi4
DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING
A.V.C COLLEGE OF ENGINEERING, MAYILADUTHURAI.
Abstract— A boost Power Factor Correction (PFC) front end converter followed by a full bridge transformer-isolated dc/dc
converter is popular in offline dc power supply. In this configuration switching losses are high and overall efficiency is
reduced. For solving this problem individual soft-switching techniques are required for both the converters. A dc power
supply system that uses a new Zero-Voltage Switching (ZVS) strategy to get ZVS function is proposed here. A soft-switching
dc power supply system with high input power factor and stable dc output voltage is presented with simple and compact
configuration. The proposed circuit is not only operated at constant frequency, but all semiconductor devices are operated
at soft switching without additional voltage stress. A significant reduction in the conduction losses is achieved, since the
circulating current for the soft switching flows only through the auxiliary circuit and a minimum number of switching
devices are involved in the circulating current path, and the rectifier in the proposed converter uses a single converter
instead of the conventional configuration composed of a four-diode front-end rectifier followed by a boost converter. An
average-current-mode control is employed in proposed dc power supply system to synthesize a suitable low-harmonics
sinusoidal waveform for the input current.
Keywords— Power Factor Correction, Zero Voltage Switching, Average-current-mode control, Harmonics.
I. INTRODUCTION
In recent years, dc power supplies have been widely used in industrial equipments, such as dc uninterruptible power supply
and telecommunications power supply, and high power factor and low input-current harmonics are mandatory performances of
the dc power supplies for satisfied agency standards such as EN61000–3-2.
Thus, the PFC must be included in dc power supply. Although the traditional passive diode rectifier/LC filter can be used to
correct the power factor and these standards are also possibly satisfied[1], the size of low-frequency inductors and capacitors
will result in the dc power supplies, which are very bulky and heavy[2]-[4]. The passive filter approach to PFC is limited to
applications where the size and weight of the converter are not major concerns. For overcoming this problem, a boost PFC
front-end converter followed by a transformer-isolated dc–dc converter is the most extensively employed in offline power
supplies[5], and full-bridge transformer-isolated dc/dc converter is the most extensively applied in medium-to-high power dc/dc
power conversion[3].
Thus, a boost PFC front-end converter followed by a full-bridge transformer-isolated dc/dc converter is the most popularly
used in offline dc power supplies. A high input power factor soft-switching single-stage dc power supply system using a ZVSpulse width modulation strategy is proposed here.
II. POWER FACTOR CORRECTION TECHNIQUES
As power electronics equipments are increasingly being used in power conversion, they inject low order harmonics into the
utility. Due to the presence of these harmonics, the total harmonic distortion is high and the input power factor is poor. Due to
problems associated with low power factor and harmonics, utilities will enforce harmonic standards and guidelines which will
limit the amount of current distortion allowed into the utility and thus the simple diode rectifiers may not in use. So, there is a
need to achieve rectification at close to unity power factor and low input current distortion.
A.
Passive power factor correction technique
In passive power factor correction techniques, an LC filter is inserted between the AC mains line and the input port of the
diode rectifier of AC/DC converter.
B.
Active power factor correction techniques
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© 2014, IJIRAE- All Rights Reserved
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International Journal of Innovative Research in Advanced Engineering (IJIRAE) ISSN: 2349-2163
Volume 1 Issue 10 (November 2014)
www.ijirae.com
In active power factor correction techniques approach, Switched Mode Power Supply (SMPS) technique is used to shape the
input current in phase with the input voltage. Thus, the power factor can reach up to unity The Active PFC techniques can be
classified as follows
1) PWM power factor correction: In PWM power factor correction approach, the power switching device operates at pulsewidth modulation mode. Basically in this technique switching frequency of active power switch is constant, but turn-on and
turnoff mode is variable.
2) Resonant power factor correction: In the resonant converter, the voltage across a switch or the current through a switch is
shaped by the resonance of inductor and capacitor to become zero at the time of turned on or off
3) Soft Switching Power Factor Correction: The soft-switching PFC technique combines the advantages of PWM mode and
resonant mode techniques with an additional resonant network consisting of a resonant inductor, a resonant capacitor and an
auxiliary switch. The PFC circuit works at constant switching frequency and the power switch turns on and off at zero current
or zero voltage conditions. Thus efficiency and power factor both improved by this technique.
III. TOPOLOGY FOR POWER FACTOR IMPROVEMENT
A high-input power factor soft-switching single-stage dc power supply system using a ZVS – PWM strategy is proposed here.
In the proposed system, the components of boost rectifier in the circuit is rearranged to provide the soft switching on all
semiconductors in the full bridge transformer-isolated dc/dc converter, and a ZVS–PWM commutation cell is used to provide
the ZVS on all semiconductors in the boost rectifier. Thus, the proposed main circuit can be simplified, and all semiconductor
devices in the proposed converter can be operated at ZVS. An average current- mode control is employed in the proposed
converter synthesize a suitable low-harmonics sinusoidal waveform for the input current. In this topology the input inductor
current wave must follow the line input voltage. In this topology angle between voltage and current becomes near to zero, so the
power factor is unity.
A. Circuit diagram
Thus circuit can be divided into three sections. The first one is the input rectifier (boost power factor
pre-regulator) that is designed to operate at PWM continuous conduction mode (CCM) and is composed of
Lin, S1, S2, D1, D2, and C1, the switches S1, S2 operating at soft switching strategy.
Fig. 1 Proposed high power factor dc power supply system
In this section can perform the functions of PFC and boost ac/dc conversion. The switches S1 and S2 are synchronously
turned on and turned off. The operation of input rectifier is the same as the conventional boost power factor pre-regulator. It
operates at fixed frequency and variable duty ratio dependent on the amplitude of line input voltage, and this duty ratio is a
sinusoidal function. The duty ratio is lower when the rectifier operates at higher amplitude of line input voltage, and it is higher
when the rectifier operates at lower amplitude of line input voltage. In this method the current of input inductor can control to
follow in the line input voltage and reduce its total harmonic distortion to get high power factor.
The second one is a ZVS–PWM commutation cell to provide the soft switching on S1, S2and other switches in the circuit.
This section composed of the auxiliary diodes Da1 and Da2, the resonant inductor Lr, the resonant capacitor Cr, the transformer
T, and auxiliary switch Sa. The third one is the full-bridge transformer-isolated dc/dc converter and is composed of the switches
S3, S4, S5, S6, D3, and D4, and the isolated transformer and output filter Lf and Cf, respectively. This section performs the
function of conventional PWM full-bridge transformer-isolated dc/dc conversion.
B. Assumptions in circuit operation
The following assumptions are made during one switching cycle.
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International Journal of Innovative Research in Advanced Engineering (IJIRAE) ISSN: 2349-2163
Volume 1 Issue 10 (November 2014)
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1) The power factor pre-regulator inductor Lin is large enough to assume that the input current ILin k is constant and it is much
greater than resonant inductor Lr.
2) The output filter inductor Lf is large enough to assume that the output current ILf is constant and is much greater than the
resonant inductor Lr.
3) The capacitorC1 is large enough to assume that the voltage VC1 is constant and ripple free.
4) The resonant voltage vCr (t) is equal to VC1 and the resonant current iLr (t) is equal to zero. Based on this assumption, circuit
operation for single cycle divided in to 24 stages. The power stage diagram and the ideal relevant wave forms during one
switching period are shown in Fig. 2 and 3.
C. Modes of operation
1) Mode 1[Fig. 2(a):t0-t1]: Before t = t0, the switches S3, S4, S5, and S6 maintain turn-ON state, and the
switches S1 and S2 maintain turn-OFF state. The energy stored in inductor Lin is delivered to the capacitor
C1 while the output loop of the dc/dc converter is in a freewheeling state. This stage begins when Sa turns
on with zero-current switching (ZCS) at t = t0. The resonant inductor Lr is charged linearly from voltage (1
− 1/k)VC1 , where k is the turn ratio of the transformer T. iLr (t) increases linearly and the stage ends when
it reaches ILin k + ILf .
2) Mode 2[Fig. 2(b):t1-t2]:During this stage, the switches S4 and S5 are turned off at ZVS when the body diodes of switches
S3, S4, S5, and S6 turn off with ZCS at t = t1. The capacitor Cr and inductor Lr have started resonant operation. vCr (t) decreases
and iLr (t) increases. The energy stored in capacitor C1 is gradually provided to the dc/dc converter. The stage ends when vCr (t)
drops to null.
3) Mode 3[Fig. 2(c):t2-t3]: In this stage, the diodes D1, D2, and the body diodes of switches S1 and S2 are turned on at ZVS.
Because the voltage across switches S1 and S2 is zero, this is the best time to turn on the switches S1 and S2 with ZVS.
In this stage, the freewheeling loop is also formed by Da1, Lr, Sa, the body diodes of S1 and S2, and the diodes D1 and D2.
Thus, the energy stored in resonant inductor Lr is delivered to the capacitor C1 via transformer T. iLr (t) decreases linearly. In
this time, the energy stored in capacitor C1 is continuously provided to the dc/dc converter and vin (t) charges the input inductor
Lin.
4) Mode 4[Fig. 2(d):t3-t4]: At t = t4, iLr (t) is equal to zero. The body diodes of the switches S1 and S2, and the diodes D1
and Da1 are naturally turned off at ZCS and this stage begins. In this stage, vin (t) charges continuously the input inductor Lin and
the energy stored in capacitor C1 is continuously provided to the dc/dc converter.
The boost power factor pre-regulator has another mission, which provides the ZVS on all semiconductors in the dc/dc
converter. Although the duty interval DPFC*kTs is not complete, the switches S1 and S2 must be turned off at t = t4 for providing
soft commutation in dc/dc converter circuit. Therefore, the switches S1 and S2 must be turned off at t = t4.
5) Mode 5[Fig. 2(e):t4-t5]: In this stage, the energy stored in input inductor Lincharges the resonant capacitor cr. Thus, vCr (t)
increases linearly and vpn (t) decreases linearly. This stage is finished when vCr (t) reaches vC1 and vpn (t) drops to zero.
6) Mode 6[Fig. 2(f):t5-t6]: In this stage, because the voltage vpn (t) drops to zero, the body diodes of the
switches S3, S4, S5, and S6 switch S4 can be turned on with ZVS. The switch S6 can be turned off with ZVS.
The freewheeling loop is formed in dc/dc converter circuit.
The energy stored in input inductor Lin is delivered to the capacitor C1.
7) Mode 7[Fig. 2(g):t6-t7]: Although this mission providing soft commutation on the switches S3 and S4 has been complete
in stage 6, the switches S1 and S2 must perform continuously the turn-ON operation of the boost power factor pre-regulator.
Therefore, the switch Sa is turned on with ZCS at t = t6 again for providing soft commutation on them, and this stage begins.
The resonant inductor Lr charges linearly from voltage (1 − 1/k)*VC1 again. iLr (t) increases linearly and the stage ends when it
reaches ILin k + ILf .
8) Mode 8[Fig. 2(h):t7-t8]: During this stage, the body diodes of switches S5 and S6 are turned off with ZCS and the dc/dc
converter circuit performs continuously the freewheeling state. The resonance of Cr and Lr is started again. vCr (t) decreases and
iLr (t) increases. The stage ends when vCr (t) drops to null.
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© 2014, IJIRAE- All Rights Reserved
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International Journal of Innovative Research in Advanced Engineering (IJIRAE) ISSN: 2349-2163
Volume 1 Issue 10 (November 2014)
www.ijirae.com
9) Mode 9[Fig. 2(i):t8-t9]: In this stage, the diodes D1 and D2, and the body diodes of switches S1 and S2 are turned on at
ZVS. Because the voltage across switches S1 and S2 is zero, the switches S1 and S2 can be turned on with ZVS again. In this
stage, the freewheeling loop is also formed by Da1, Lr, and Sa, the body diodes of S1 and S2, and the diodes D1 and D2.
Fig. 2 Modes of operation
10) Mode 10[Fig. 2(j):t9-t10]: At t = t9, the body diodes of the switches S1 and S2, and the diodes D1 and Da1 are turned off
at ZCS and this stage begins. In this stage, the input voltage vin (t) charges continuously the input inductor Lin. This stage ends
when the duty interval DPFCkTs is completed and the switches S1 and S2 are turned off at t = t10.
11) Mode 11[Fig. 2(k):t10-t11]: In this stage, the energy stored in input inductor Lin charges the resonant capacitor Cr. Thus,
vCr (t) increases linearly and vpn (t) decreases linearly. This stage is finished when vCr (t) reaches VC1 and vpn (t) drops to zero.
12) Mode 12[Fig. 2(l):t11-t12]:In this stage, because vpn (t) drops to zero, the body diodes of the switches S1, S2, S3, and S4,
and the switches S5 and S6 can be turned on with ZVS. The dc/dc converter circuit performs continuously the freewheeling state.
The energy stored in input inductor Lin is delivered to the capacitor C1.
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© 2014, IJIRAE- All Rights Reserved
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International Journal of Innovative Research in Advanced Engineering (IJIRAE) ISSN: 2349-2163
Volume 1 Issue 10 (November 2014)
www.ijirae.com
Fig. 3 ideal relevant wave form
The operation principles of stages 13–24 are the same as stages 1–12 except that the play role of the switches S3, S4, S5, and
S6 in circuit operation is changed. After stage 24, the circuit operation is returned to the first stage.
III. PERFORMANCE INVESTIGATION BY MATLAB SIMULATION
The performance of dc power supply system is investigated by means of detailed MATLAB simulation.
A)
Simulation model of open loop system
Simulation model of open loop system is shown in Fig. 3
In this circuit, the input voltage is 110Vrms and input current is 11A. We get output voltage of 48V and
current 21A. The power factor gets improved to 0.99
Fig. 4 Open loop simulation model
B)
Simulation model for closed loop system
Simulation model of closed loop system is shown in Fig. 4 In this circuit, the input voltage is 110Vrms
and input current is 11A.
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International Journal of Innovative Research in Advanced Engineering (IJIRAE) ISSN: 2349-2163
Volume 1 Issue 10 (November 2014)
www.ijirae.com
Fig. 5 Simulation model for closed loop system
We get output voltage of 47.35V and current 25A. The power factor is improved to 0.99. Average
current control method is used to control the closed loop system.
C)
Simulation results for open and closed loop system
1) Voltage, current and power: Input and output voltage, current and power wave forms are carried
out by MATLAB simulation for both open loop and closed loop systems. Corresponding wave forms are
shown in following figures.
Fig. 6 Input voltage and current(open&closed loop)
Fig. 6 shows the input voltage and current waveforms of both open loop and closed loop system. In
these waveforms the current is in phase with voltage, the angle between the voltage and current becomes
nearly zero. So the power factor value is almost unity.
Fig. 7(a) Output voltage and current(open loop)
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International Journal of Innovative Research in Advanced Engineering (IJIRAE) ISSN: 2349-2163
Volume 1 Issue 10 (November 2014)
www.ijirae.com
Fig. 7(b) Output voltage and current(closed loop)
Fig. 7(a) & (b) shows the output voltage and current for open loop and closed loop system. From this
we observed that voltage and current value are of 48V and 21.5A for open loop system and, 48V and 24A
for closed loop system.
Fig. 8(a) & (b) shows input/output power for open loop system. From this we observed that
input/output power values are 1040W and 1016W for open loop system
Fig. 9(a) & (b) shows input/output power for closed loop system. From this we observed that
input/output power values are 1189W and 1189W for closed loop system.
Fig. 8(a) Input power(open loop)
Fig. 8(b) Output power(open loop)
Fig. 9(a) Input power(closed loop)
Fig. 9(b) Output power(closed loop)
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International Journal of Innovative Research in Advanced Engineering (IJIRAE) ISSN: 2349-2163
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1) Power factor and efficiency: Power factor and efficiency are measured from the open loop and
closed simulation models.
Fig. 10(a) Power factor and efficieny(open loop)
Fig. 10(b). Power factor and efficieny(closed loop)
Fig. 10(a) & (b) shows power factor and efficiency for open loop and closed loop systems. The power factor has been
improved to 0.99 in both open loop as well as in closed system, and it is evident from the observations that there is also
betterment in efficiency for both open and closed loop configurations.
IV.
CONCLUSION
A soft switching single phase dc power supply with high input power factor and stable dc output voltage is designed by
using MATLAB simulation software. This dc power supply system is applicable in dc uninterrupted power supply system
design. This proposed dc power supply system operating at constant frequency and all semiconductor devices with soft
switching strategy. In this proposed system significant reduction in voltage stress and conduction losses are achieved. Power
factor and efficiency is improved compared with conventional topology.
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